In dielectric drying systems particularly those for drying wood of the type described in U.S. Pat. No. 3,968,268 issued Oct. 19, 1976 to Koppelman, it is conventional practice to estimate the moisture content of the drying load by measuring the volume of water or condensate exiting the drying system (as mentioned by Koppelman). It is common for equipment of this type to operate in a nearly closed cycle where water extracted from the drying load is discharged from the bottom of the drying chamber and from a condensing system. Depending on the condensing system and changing operating conditions, a varying amount of unaccounted water vapor may be released into the environment.
Of greater concern, much larger moisture content measurement inaccuracies are introduced by not knowing with any great degree of certainty the initial moisture of the drying load. With wood products, the initial moisture contents of drying loads often have large variations which depend on a number of factors such as from where the wood was harvested, the time of year, the wood species, sapwood/heartwood differences, and how long the wood has been air drying prior to kiln drying. Given the inherent variability of wood products, it is clear that moisture content measurement using this current technique is full of uncertainty and inaccuracy.